Consolidating financial information by industry segment (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues:
Self-moving equipment rentals	$ 1,069,405	$ 1,162,025	$ 2,068,611	$ 2,252,800
Self-storage revenues	208,890	185,586	407,851	358,763
Self moving and self-storage products and service sales	91,571	96,864	192,443	206,215
Property management fees	9,267	9,277	18,444	18,416
Life insurance premiums	22,498	25,456	45,629	51,237
Property and casualty insurance premiums	25,571	25,718	45,893	45,690
Net investment and Interest income	64,738	30,509	129,330	64,082
Other revenue	157,920	167,429	281,967	303,501
Total revenues	1,649,860	1,702,864	3,190,168	3,300,704
Costs and expenses:
Operating expenses	835,258	811,594	1,598,499	1,544,761
Commission expenses	111,961	125,341	218,888	243,834
Cost of sales	66,620	72,625	137,295	152,296
Benefits and losses	42,553	39,512	87,897	79,269
Amortization of deferred policy acquisition costs	6,826	6,972	14,871	14,644
Lease expense	8,450	7,684	16,033	15,159
Depreciation, net of (gains) losses on disposals	154,122	117,318	291,936	231,114
Net (gains) losses on disposal of real estate	1,715	1,872	2,736	4,179
Total costs and expenses	1,227,505	1,182,918	2,368,155	2,285,256
Earnings (loss) from operations before equity in earnings of subsidiaries	422,355	519,946	822,013	1,015,448
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	422,355	519,946	822,013	1,015,448
Other components of net periodic benefit costs	(364)	(304)	(729)	(608)
Interest expense	(63,943)	(57,193)	(124,541)	(106,992)
Fees and amortization on early extinguishment of debt	0	(959)	0	(959)
Pretax earnings	358,048	461,490	696,743	906,889
Income tax expense	(84,540)	(111,624)	(166,397)	(218,678)
Earnings available to common stockholders	273,508	349,866	530,346	688,211
Operating Segments [Member] | Moving and Storage Consolidations [Member]
Revenues:
Self-moving equipment rentals	1,070,688	1,163,376	2,070,767	2,255,086
Self-storage revenues	208,890	185,586	407,851	358,763
Self moving and self-storage products and service sales	91,571	96,864	192,443	206,215
Property management fees	9,267	9,277	18,444	18,416
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	0	0	0	0
Net investment and Interest income	28,520	15,077	55,815	20,017
Other revenue	156,642	166,678	279,771	301,959
Total revenues	1,565,578	1,636,858	3,025,091	3,160,456
Costs and expenses:
Operating expenses	820,617	796,498	1,568,900	1,516,292
Commission expenses	111,961	125,341	218,888	243,834
Cost of sales	66,620	72,625	137,295	152,296
Benefits and losses	0	0	0	0
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	8,839	8,261	16,941	16,181
Depreciation, net of (gains) losses on disposals	154,122	117,318	291,936	231,114
Net (gains) losses on disposal of real estate	1,715	1,872	2,736	4,179
Total costs and expenses	1,163,874	1,121,915	2,236,696	2,163,896
Earnings (loss) from operations before equity in earnings of subsidiaries	401,704	514,943	788,395	996,560
Equity in earnings of subsidiaries	16,862	3,906	27,092	15,915
Earnings from operations	418,566	518,849	815,487	1,012,475
Other components of net periodic benefit costs	(364)	(304)	(729)	(608)
Interest expense	(64,199)	(57,459)	(125,048)	(107,520)
Fees and amortization on early extinguishment of debt		(959)		(959)
Pretax earnings	354,003	460,127	689,710	903,388
Income tax expense	(80,495)	(110,261)	(159,364)	(215,177)
Earnings available to common stockholders	273,508	349,866	530,346	688,211
Operating Segments [Member] | Property and Casualty Insurance [Member]
Revenues:
Self-moving equipment rentals	0	0	0	0
Self-storage revenues	0	0	0	0
Self moving and self-storage products and service sales	0	0	0	0
Property management fees	0	0	0	0
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	26,371	25,960	47,418	46,790
Net investment and Interest income	5,481	(2,597)	12,273	(345)
Other revenue	0	0	0	0
Total revenues	31,852	23,363	59,691	46,445
Costs and expenses:
Operating expenses	12,113	11,576	23,420	21,770
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	4,229	6,075	8,687	10,454
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	91	26	183	184
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0	0	0	0
Total costs and expenses	16,433	17,677	32,290	32,408
Earnings (loss) from operations before equity in earnings of subsidiaries	15,419	5,686	27,401	14,037
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	15,419	5,686	27,401	14,037
Other components of net periodic benefit costs	0	0	0	0
Interest expense	0	0	0	0
Fees and amortization on early extinguishment of debt		0		0
Pretax earnings	15,419	5,686	27,401	14,037
Income tax expense	(3,181)	(1,167)	(5,653)	(2,922)
Earnings available to common stockholders	12,238	4,519	21,748	11,115
Operating Segments [Member] | Life Insurance [Member]
Revenues:
Self-moving equipment rentals	0	0	0	0
Self-storage revenues	0	0	0	0
Self moving and self-storage products and service sales	0	0	0	0
Property management fees	0	0	0	0
Life insurance premiums	22,498	25,456	45,629	51,237
Property and casualty insurance premiums	0	0	0	0
Net investment and Interest income	31,621	19,041	63,132	46,429
Other revenue	1,403	1,199	2,442	2,133
Total revenues	55,522	45,696	111,203	99,799
Costs and expenses:
Operating expenses	4,731	5,558	10,097	10,667
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	38,324	33,437	79,210	68,815
Amortization of deferred policy acquisition costs	6,826	6,972	14,871	14,644
Lease expense	33	26	61	54
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0	0	0	0
Total costs and expenses	49,914	45,993	104,239	94,180
Earnings (loss) from operations before equity in earnings of subsidiaries	5,608	(297)	6,964	5,619
Equity in earnings of subsidiaries	0	0	0	0
Earnings from operations	5,608	(297)	6,964	5,619
Other components of net periodic benefit costs	0	0	0	0
Interest expense	(120)	(120)	(240)	(240)
Fees and amortization on early extinguishment of debt		0		0
Pretax earnings	5,488	(417)	6,724	5,379
Income tax expense	(864)	(196)	(1,380)	(579)
Earnings available to common stockholders	4,624	(613)	5,344	4,800
Consolidation, Eliminations [Member]
Revenues:
Self-moving equipment rentals	(1,283)	(1,351)	(2,156)	(2,286)
Self-storage revenues	0	0	0	0
Self moving and self-storage products and service sales	0	0	0	0
Property management fees	0	0	0	0
Life insurance premiums	0	0	0	0
Property and casualty insurance premiums	(800)	(242)	(1,525)	(1,100)
Net investment and Interest income	(884)	(1,012)	(1,890)	(2,019)
Other revenue	(125)	(448)	(246)	(591)
Total revenues	(3,092)	(3,053)	(5,817)	(5,996)
Costs and expenses:
Operating expenses	(2,203)	(2,038)	(3,918)	(3,968)
Commission expenses	0	0	0	0
Cost of sales	0	0	0	0
Benefits and losses	0	0	0	0
Amortization of deferred policy acquisition costs	0	0	0	0
Lease expense	(513)	(629)	(1,152)	(1,260)
Depreciation, net of (gains) losses on disposals	0	0	0	0
Net (gains) losses on disposal of real estate	0	0	0	0
Total costs and expenses	(2,716)	(2,667)	(5,070)	(5,228)
Earnings (loss) from operations before equity in earnings of subsidiaries	(376)	(386)	(747)	(768)
Equity in earnings of subsidiaries	(16,862)	(3,906)	(27,092)	(15,915)
Earnings from operations	(17,238)	(4,292)	(27,839)	(16,683)
Other components of net periodic benefit costs	0	0	0	0
Interest expense	376	386	747	768
Fees and amortization on early extinguishment of debt		0		0
Pretax earnings	(16,862)	(3,906)	(27,092)	(15,915)
Income tax expense	0	0	0	0
Earnings available to common stockholders	$ (16,862)	$ (3,906)	$ (27,092)	$ (15,915)